A conventional rotary encoder is described with reference to FIGS. 11 and 12.
FIG. 11 is a sectional view of a conventional rotary encoder. The conventional encoder includes base 1 having concentric circular comb-like contact 3 as a fixed element on the inner top face thereof, and case 2 covering the top face of the base. Housed in a space formed by the case 2 and the base 1 is rotating body 5 that holds resilient contact 4 for engaging with comb-like contact 3 to generate an electric signal.
Straight rod-like rotating shaft 6 has upper portion 6A, intermediate portion 6B, and lower portion 6C. Intermediate portion 6B is rotatably supported by cylindrical bushing 7 in the upper portion of case 2. Upper portion 6A protruding upwardly from bushing 7 is covered with control knob 8. The rotating body 5 is joined by caulking to lower portion 6C protruding into the space formed by the case and the base. Connecting fitting 9 fastens base 1 and case 2.
Next, the operation of this rotary encoder is described with reference to FIG. 12 for explaining how the elements are engaged with each other. When knob 8 is rotated, rotating shaft 6 and rotating body 5 make rotary motion with the circular hole through bushing 7 as center. This brings the tip of resilient leg 4A held by rotating body 5 into resilient sliding contact with comb-like contact 3. Thereby, a pulse signal corresponding to the rotary manipulation is output from terminal 10 connected to comb-like contact 3.
In recent years, progress in performance as well as downsizing and high-density has been made mainly in portable electronic equipment. This necessitates smaller electronic components having higher performance. Especially for electronic components for use in the control part of portable electronic equipment, a small height including a control knob thereof and high precision are required.
However, for the conventional rotary encoder, in order to reduce the height including knob 8 without changing the dimension of a body portion that houses the elements of the electronic component, length L1 of bushing 7 (see FIG. 11) must be reduced. This is because the conventional rotary encoder is structured so that rotating shaft 6 is supported by bushing 7 of case 2 that constitutes the body portion housing the elements, and upper portion 6A is covered with knob 8.
On the other hand, a gap of approx. 0.03 mm must be provided between the outer diameter of intermediate portion 6B and the inner diameter of the cylindrical hole through bushing 7 that rotatably supports rotating shaft 6. Thus, reducing length L1 of bushing 7 reduces the length over which rotating shaft 6 is supported and increases the runout of rotating shaft 6. Therefore, knob 8 provided over upper portion 6A makes more back-lashes. As a result, there are problems: the operational sensation deteriorates and resilient contact 4 held by rotating body 5 that is fixed to lower portion 6C makes misregistration, although it is small.